1. Technical Field
The invention relates to an exposure head that exposes a to-be-exposed surface such as a latent image carrier, an image forming apparatus using the exposure head, and an image forming method.
2. Related Art
In the related art, there are disclosed exposure heads, in which an image forming optical system forms an image by using light from a plurality of light-emitting element light-emitting elements so as to expose a surface (to-be-exposed surface) of a latent image carrier. For example, in an exposure head disclosed in JP-A-2005-096259, a plurality of light-emitting elements are aligned in a main scan direction, and an image forming optical system form an image by using light from the light-emitting elements, so that spots are formed. Therefore, a plurality of the spots are formed to be aligned in the main scan direction, and a surface of a latent image carrier is exposed by the spots, so that a one-line latent image is formed in the main scan direction. In addition, the light-emitting elements repetitively emit light at timings according to movement of the surface of the latent image container in a sub scan direction perpendicular to the main scan direction, so that a plurality of the aforementioned one-line latent images are formed in the sub scan direction. As a result, a one-page latent image is formed.
As the light-emitting element, a LED (Light Emitting Diode) device or an organic EL (Electro-Luminescence) device may be used. However, these devices are worn out due to many times of light emitting, so that the devices may not emit a sufficient light amount to form the latent image. In the exposure head disclosed in JP-A-2005-096259, a plurality of light-emitting elements are further disposed to correspond to the aforementioned plurality of light-emitting elements in one-to-one correspondence. In other words, two or more light-emitting elements are disposed to be aligned in the sub scan direction, and one of the light-emitting elements is selectively used for the exposing operation. In addition, when the selected one of the light-emitting elements is exhausted, the light-emitting element used for the exposing operation is changed over. Accordingly, the life cycle of the exposure head can be prolonged.
The two or more light-emitting elements that are aligned in the sub scan direction form spots at different positions in the sub scan direction. Accordingly, before and after the changeovers of the light-emitting elements, the forming positions of the spots are changed. As a result, before and after the changeovers of the light-emitting elements, a shift in the latent image forming position on the surface of the latent image container occurs in the sub scan direction, so that a good latent image may not be formed.